Integrated blower diffuser-fin heat sink

ABSTRACT

An air-cooled heat exchange device for cooling an object such as an electronic device generating heat during use. The device includes a toroidal electric motor with a centrifugal blower for directing air flow in a downward and outward direction, a heat sink positioned to receive the air flow from the blower; and a spiral diffuser as part of the heat sink, the diffuser having vanes for directing the air flow spirally over the heat sink. The vanes may include microfabricated vibrating reeds and a plurality of microfabricated dimples on at least some of the vanes.

STATEMENT OF GOVERNMENT INTEREST

The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of [Contract No. or Grant No.] ______ awarded by Defense Advanced Research Projects Agency/Microsystems Technology Office.

BACKGROUND

The present invention relates to air-cooled heat-exchange systems used to remove heat from electronic devices that generate heat during operation.

Over the past 40 years, many electronic technologies such as telecommunications, and active sensing and imaging have undergone tremendous technological innovation. During this same time, the technologies, designs and performance of air-cooled heat exchangers has remained fundamentally unchanged. Performance data for present day heat exchangers and blowers is based on that old technology.

Because of the improved performance and increased power consumption of electronic technologies, heat rejection systems have grown in size, weight, complexity and cost. In some instances, conventional air-cooled heat sinks have become inadequate. This has resulted in more exotic liquid-cooled manifolds, spray-cooled enclosures, and vapor-compression refrigeration being proposed. All these newly proposed cooling approaches add complexity associated with operation of active pumps and compressors, as well as the need to prevent fluid or vapor leakage. Reliability of those approaches has not been demonstrated at this time.

Conventional designs rely on high heat transfer impingement flows generated by axial fans placed above the heat sink. Airflow at the fan outer diameter passes over a portion of the available heat transfer area, thus requiring high airflow rates and high fan power input.

SUMMARY

An integrated centrifugal blower-diffuser with a vaned heat-sink provides cooling of electronics and other devices that generate heat during use. Airflow is introduced radially onto the heat sink such that the centrifugal blower and fin-diffuser direct the bulk of the airflow outward across the available heat transfer area of the device. Air is induced through space in the shaft of an electric motor, and the air is then accelerated centrifugally through a set of rotating impellor vanes, and then diffused radially through a set of radial heat sink fins. The radial heat sink fins form the spiral diffuser fins (or vanes) to provide pressure recovery within the heat sink. This enables tight intra-vane spacing and increased heat transfer surface area.

The device may also include passive vanes, surface features and microfabricated active elements to provide heat transfer enhancement at reduced air flow rates, thus providing reduced thermal resistance of the heat sink device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an integrated blower and diffuser.

FIG. 2 is a partially cut away view of the devices in FIG. 1.

FIG. 3 is a side sectional view of the device in FIG. 1.

FIG. 4 is a top section view of the device in FIG. 1.

FIG. 5 is a view showing stationary vanes and active fin elements of the device shown in FIG. 1.

DETAILED DESCRIPTION

Air cooling system 10 for cooling component C is shown in FIG. 1. System 10 includes motor 11, blower 13, cover 14, diffuser 15 and heat sink base 17. The heat sink base 17 may be an integral part of system 10, or it may be part of component C being cooled. In FIG. 1, the diffuser 15 also functions with heat sink base 17 as part of a heat sink. The motor 11 and blower 13 are integral and are mounted on cover 14, which also serves as the top of the diffuser 15 and supports all of the elements between cover 14 and heat sink base 17. System 10 cools objects it is in heat transfer contact with, such as an electronic device shown generically as component C. Any object generating heat can be cooled by system 10 if it can be placed in heat transfer contact therewith.

Motor 11 is shown as a toroidal electric motor with a central airway 12 around its rotational axis. Air is drawn by rotation of blower 13 axially down through central airway 12 into blower 13 and then into diffuser 15. Air flows outward. Other motors may also be used, with different configurations and sources of power, depending on the size and shape of the object to be cooled. Controller 31 provides a source of energy via line 29 to drive motor 11 and other active components described below. In operation, motor 11 causes air to be drawn into central airway 12 by blower 13, passing through a central aperture in cover 14 into diffuser 15. The air flows through diffuser 15 and in contact with heat sink base 17 to cool component C. Airflow through diffuser 15 can be radial, spiral or diffuser 15 can be configured for other paths.

As seen in FIG. 2, the internal components of system 10 are shown. Motor 11 includes a housing 11 a, bearings 18, permanent magnet rotor 19, stator 20, and stator windings 20 a to support rotation of the rotor 19 and blower 13. Stator winding 20 a are positioned to receive electrical power from controller 31 and drive the blower 13 in a normal electric motor fashion.

Blower 13 has an upper hub 13 a, lower hub 13 b and blades 16. Upper hub 13 a is connected to the permanent magnet rotor 19. Blades 16 have an upper end 16 a connected to lower hub 13 b. A center port 13 c in lower hub 13 b provides a passage for air flow through lower hub 13 b and into space between lower hub 13 b and heat sink base 17.

Diffuser 15 includes a plurality of fins or vanes 23 and other elements shown and described below that take air from central passage 12 so that air contacts the vanes 23 and the heat sink base 17 to absorb heat into the air and out of system 10. Diffuser 15 serves two purposes in this device. First, diffuser 15 deflects the flow of air from a vertically downward direction radially outward as will be described below, Second, the diffuser vanes 23 provide additional heat conductive material as part of the heat sink 17, so that more hot metal is exposed to the cooling air flow. This is a significant improvement over conventional designs that simply direct the air flow axially to impinge on a heat sink. The motor 11, blower 13, diffuser 15 and heat sink 17 are attached together to form a single device that can be attached to an electronic package such as a circuit board in the same manner that conventional air-cooled heat-exchangers are attached.

Air flow in FIG. 3 is pulled down into system 10 central airway 12 by blower blades 16 into a radial direction. This air passes through the channels formed by vanes 23, transferring heat from the heat sink 17 and from vanes 23 into the air as it flows out of system 10, and, accordingly, cooling the object on which heat sink 17 is positioned. Vanes 23 are made from heat conductive materials such as metals. Aluminum and copper vanes are effective conductors. System 10 is compact and yet provides a great increase in the surface area of the heat sink.

FIG. 4 is another view of the relationship of the blower blades 16, the heat sink base 17 and the vanes 23, and illustrates the spiral configuration of the vanes 23. Air is drawn by blower blades 16 through central passage 12 and down into the diffuser 15. Diffuser 15 also include secondary vanes or splitter plates 23 a and 23 b at the ends of the channels formed by vanes 23 and mounted on vanes 23 to narrow the channel and further disrupt air flow and improve heat transfer. Also seen in FIG. 4 are a plurality of posts 25 that support reeds 27 for further disruption of the air flow and thus further heat transfer and cooling. Posts 25 are supported between cover 14 and heat sink base 17. Reeds 27 may be passive or active, as described below.

In addition to the basic flow pattern as seen in FIGS. 3 and 4, FIG. 5 illustrates several additional ways to improve the cooling of the device. Vanes 23 have been further modified to decrease fin-to-air heat transfer resistance by the use of microfabricated dimples 24, seen in FIG. 5. Dimples 24 are created through a bipolar anodization process that has been shown to enhance air side heat transfer by from about 10% to about 30% over undimpled vanes. Other method of putting dimples 24, or other surface irregularities can be used.

FIG. 5 also illustrates the placement of vanes 23 with respect to splitter plates 23 a and 23 b to provide a larger quantity of heat conductive material in contact with the flowing air. The splitter plates 23 a and 23 b of vane 23 decrease the channel width. This increases the resistance to flow and increases heat transfer. Splitter plates 23 a and 23 b are made from heat conductive materials and may be made from the same or different materials as supporting vanes 23.

In FIG. 5, two vanes 23 are shown with post 25 for mounting reeds 27, although reeds 27 are only visible in FIG. 5 for the vane on the left. FIG. 4 shows the plurality of vanes 23, ends 23 a and 23 b, posts 25 and reeds 27. Post 25 is supported by cover 14 and heat sink base 17, as noted above. Post 25 contains a piezoelectric component that excites reeds 27 to vibrate, or reeds 27 may be piezoelectric elements.

Reeds 27 are designed to function as vibrating reeds in the space between adjacent fins to further improve heat transfer. In one embodiment, reeds 27 are formed from a silicon material having a piezoelectric component bonded to the silicon so that when the piezoelectric component is actuated by an electric signal in wire 29 from controller 31 in FIG. 1, the reed 27 vibrates. The signal driving the piezoelectric component may be the same signal driving motor 11 or it may be a different signal. The appropriate signal in wire 29 is directed to all the reeds 27 by a printed circuit on cover 14 to the post 25 that also has an electronic circuit printed thereon. Hard wiring is also an alternative method for exciting the piezoelectric component. Vibrating reed 27 introduces a high frequency, unsteady flow within the channels formed by fins 23 that greatly enhances air mixing and heat transfer from the fin wall 23 to the air flowing through them. Use of vibrating fins or reeds 27 has been shown to increase heat transfer coefficients downstream by more than 50% with only a negligible increase in the power requirement and pressure drop.

The combination of dimples 24 on vanes 23, splitter plates 23 a and 23 b, and the vibrating reeds 27 function as highly integrated active fin, and operate through the introduction of high frequency, unsteady flow within the channels formed by them. This greatly enhances mixing and heat transfer from their walls to the air. This well-mixed air is swept through the thus formed channels by the bulk airflow provided by the blower 13.

A simulated comparison between the present system described above and in the figures and a conventional air-cooled exchanger system shows significant improvement achieved by the present invention.

A conventional device has a thermal resistance of 0.2° C./W, which gives a temperature rise of 230° C., which is above the allowed operating temperature of many electronic devices. The system of this invention is estimated to have a thermal resistance of 0.05° C./W, resulting in a theoretical temperature rise of only 50° C. The system would be usable with many more electronic devices. The Coefficient of Performance (COP) is the electronic device power dissipation divided by the blower and heat sink power. For the conventional system, the COP is 100. Simulated results for the system of this invention is estimated to produces a COP of as low as 30, which results in an estimated power consumption reduction of more than a factor of three. These results are due to the substantial reduction in the airflow and increasing the back-pressure on the blower. This significantly improves operating point efficiency as well as providing a reduction in thermal resistance.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. 

1. An air-cooled heat exchange device for cooling an object, comprising: a centrifugal blower for directing air flow in a downward and outward direction; a heat sink base positioned to receive the air flow from the blower; and a diffuser on the heat sink base and in the path of the air flow from the blower, the diffuser having vanes that are in thermal communication with the heat sink base and that direct the air flow from the blower outward over the heat sink base.
 2. The device of claim 1, where the object being cooled is an electronic device generating heat during use, the electronic device being positioned in contact with the heat sink.
 3. The device of claim 1, wherein the centrifugal blower is driven by a torriodal electric motor and the downward direction is through the center of the motor.
 4. The device of claim 1, wherein the diffuser further includes secondary vanes in the air flow channels defined by the vanes to prevent flow separation and increase heat transfer surface area.
 5. The device of claim 1, wherein the vanes comprise a diffuser set of vanes forming air flow channels above the heat sink extending spirally out from the center of the heat sink.
 6. The device of claim 1, wherein the diffuser further includes vibrating reeds in the vane channels defined by the vanes.
 7. The device of claim 6, wherein the vibrating reeds include a piezoelectric component and means for actuating it to cause the reeds to vibrate.
 8. The device of claim 1, which further includes a plurality of microfabricated surface features on at least some of the vanes to increase heat transfer area per unit volume.
 9. The device of claim 8 where the plurality of microfabricated surface features are dimples.
 10. The device of claim 1, wherein the centrifugal blower extends downward into and is surrounded by the diffuser.
 11. The device of claim 10, wherein the centrifugal blower includes an upper hub, a lower hub, and a plurality of blades connected between the upper hub and the lower hub.
 12. The device of claim 11, wherein the lower hub includes a port for allowing passage of air downward through the lower hub into a space between the lower hub and the heat sink base.
 13. The device of claim 11 and further comprising a toroidal electric motor mounted on the diffuser and having a stator, a rotor, and a central air passage, the rotor being connected to the upper hub of the centrifugal blower.
 14. A method of cooling an object using an air-cooled heat exchanging device, comprising the steps of: directing air flow in a downward and outward direction using a blower; and directing the air flow through a diffuser in thermal communication with a heat sink base positioned to receive the air flow from the blower and directing it outward over the heat sink base.
 15. The method of claim 14, wherein the object being cooled is an electronic device generating heat during use, the electronic device being positioned in contact with the heat sink.
 16. The method of claim 14, wherein the centrifugal blower is a torroidal electric motor and the downward direction is through the center of the motor.
 17. The method of claim 14, wherein the diffuser vains comprises a set of vanes forming air flow channels above the heat sink extending radially out from the center of the heat sink.
 18. The method of claim 17, which further includes secondary vanes on the outer ends of the vanes to prevent separation of airflow and increase heat transfer surface area.
 19. The method of claim 17, which further includes vibrating reeds in the flow channels.
 20. The method of claim 19, wherein the vibrating reeds include a piezoelectric component for causing the reeds to vibrate.
 21. The method of claim 17, which further includes a plurality of microfabricated surface features on at least some of the vanes to increase heat transfer area per unit volume.
 22. The method of claim 21 where the plurality of microfabricated surface features are dimples. 